Reference is made FIG. 1 showing a conventional regulator circuit 10. The circuit 10 includes a power transistor 12 having a first conduction terminal coupled to a voltage supply node (Vin) and a second conduction terminal coupled to an output node (Vout). The power transistor 12 may comprise either an n-channel MOSFET device (where the first conduction terminal is the drain node and the second conduction terminal is the source node) or a p-channel MOSFET device (where the first conduction terminal is the source node and the second conduction terminal is the drain node). A control terminal of the power transistor (for example, the gate node of the MOSFET device) is driven with a gate voltage Vgate by the output of a unity gate voltage buffer circuit 14. An input of the buffer circuit 14 is coupled to the output of an error amplifier circuit 16 which generates an error signal Vc. The error amplifier circuit 16 may, for example, comprise a differential amplifier (such as an OP-AMP) having a first input coupled to receive a reference voltage (Vref) and a second input coupled to receive a feedback voltage (Vfb). In the implementation using an n-channel power transistor 12, the first input is the non-inverting input of the amplifier circuit 16 and the second input is the inverting input. Conversely, in the implementation using a p-channel power transistor 12, the first input is the inverting input of the amplifier circuit 16 and the second input is the non-inverting input. A feedback circuit network 18 is coupled between the output node Vout and the second input of the amplifier circuit 16. The feedback circuit network 18 may, for example, comprise a resistive divider circuit formed by series connected resistors R1 and R2.
The circuit 10 takes advantage of negative feedback to obtain a stable voltage output (Vout) for the load (LOAD) over a certain output current range. A load capacitor 20 is provided at the output node Vout to reduce the output noise and improve transient response. It is not difficult to compensate the negative feedback stability for a selected output capacitor over small load current range. However, it is difficult to obtain the compensation if the load current varies over a large range. In application, the load current may significantly over different operating scenarios. The load current may vary from tens of milliamperes to several amperes during normal operation, while during a low power standby mode, the load current may be as low as several microamperes. The circuit 10 of FIG. 1 is not capable of operating over such a range of load current.
To provide for greater flexibility in application, there is a need in the art for an improved regulator circuit that is capable of handling a large range of load current.